Health Risks from Exposure to Low Levels of Ionizing Radiation
Ionizing radiation, like other toxic hazards, has detrimental health effects, including cancer, at high doses and high dose rates. There is however, considerable controversy regarding the health effects of low-level radiation, at or below typical natural background levels.
Current "risk per exposure" ratios have been derived from a study of the health of atomic bomb survivors at Hiroshima and Nagasaki. These survivors received tens to hundreds of rem instantaneous (acute) exposure from the initial explosions, plus long-term (chronic) exposure from fallout.
Various regulatory bodies, including the U.S. Environmetal Protection Agency (EPA) have extrapolated these risk ratios, based on high doses, down to much lower dose levels, and all the way down to zero dose. This theoretical extrapolation is called the linear-no-threshold (LNT) hypothesis. In effect, it postulates that even the smallest incremental dose of radiation has an associated small risk associated with it.
Proponents of the theoretical LNT model argue that, since we do not know much about health effects at very low doses, it is prudent and conservative to presume that they exist, and that the LNT model represents a reasonable upper bound for the risks.
Opponents of the theoretical LNT argue that it is not supported by scientific evidence of health effects at very low doses, and that regulations based on the LNT do not achieve any real measurable public health benefit.
The following links expand on this brief introduction.
- Radiation Risk. A briefing (47 pages) on risks in everyday life, background radiation, and radiation risk.
- American Nuclear Society Position Statement on "Health Effects of Low-Level Radiation." Excellent summary of existing reseach on low level radiation effects with 72 references. It concludes, "... there is insufficient scientific evidence to support the use of the Linear No Threshold hypothesis in the projection of the health effects of low-level radiation." June 2001.
- Health Physics Society Position Statement on "Radiation Risk in Perspective." It states, "Below 5–10 rem (which includes occupational and environmental exposures), risks of health effects are either too small to be observed or are nonexistent.." August 2004.
- National Academy of Sciences, BEIR V, "Health Effects of Low Levels of Ionizing Radiation." BEIR V states that populations that reside in areas of elevated background radiation have not shown an associated increase in the risk of cancer.
- National Academy of Sciences, BEIR VII, "Health Risks from Exposure to Low Levels of Ionizing Radiation." BEIR VII states that at doses of 100 mSv (10,000 mrem) or less, statistical limitations make it difficult to evaluate cancer risk in humans. Nevertheless BEIR VII confirmed the validity of the LNT model and recommends its continued use.
- General Accounting Office Report on Radiation Standards. This report concludes that there is lack of conclusive evidence of low level radiation effects below total exposures of 5,000 to 10,000 millirem, and therefore there is no public health difference between the NRC's 25 mrem/y standard and the EPA's 15 mrem/y standard. Testimony before the U.S. Senate.
- NRC SECY-96-110, Completion of Response to the Staff Requirements Memorandum, for SECY-95-249, on Risk Harmonization White Paper and Recommendations by the Interagency Steering Committee on Radiation Standards. This 1996 NRC staff paper compares theoretical radiation and chemical risks, in particular background levels of radiation and chemical risks.
- Radiation Risk and Ethics. by Zbigniew Jaworowski (Reprinted with permission from Physics Today, 52(9), September 1999, pp. 24-29, American Institute of Physics.). Examines the rationale and fallacy of the linear non-threshold model of radiation risk.
- How to Explain Radiation Risk. Washington State Department of Health.